1. Field of the Invention
The present invention relates generally to cutting elements for use on earth-boring drill bits and bits so equipped. In particular, the present invention relates to cutting elements having abrasive particles impregnated in a matrix. More specifically, the cutting elements of the present invention may include a tough and ductile support structure which may be internal or external to the impregnated segment. Yet more specifically, cutting elements, and segments, embodying the present invention may be arranged in preselected arrays, or patterns, and orientations to enhance drilling efficiency.
2. Background of Related Art
Conventionally, earth-boring drill bits with impregnated cutting structures, commonly termed xe2x80x9csegments,xe2x80x9d have been employed to bore through hard and abrasive formations, such as basalt, dolomite and hard sandstone. As depicted by FIG. 1, the impregnated segments 16 of such drill bits are typically secured to the boring end 14, which is typically termed the xe2x80x9cface,xe2x80x9d of the bit body 12 of the drill bit 10 in a generally radial fashion. Impregnated segments may also be disposed concentrically over the face of the drill bit. As the drill bit gradually grinds through a very hard and abrasive formation, the outermost layer of the impregnated segments containing abrasive particles (such as small diamonds, diamond grit, or other superabrasive particles such as cubic boron nitride) wear and may fracture. Many conventional impregnated segments are designed to release, or xe2x80x9cshed,xe2x80x9d such diamonds or grit in a controlled manner during use of the drill bit. As a layer of diamonds or grit is shed from the face, underlying diamonds are exposed as abrasive cuttings and the diamonds that have been shed from the drill bit wear away the exposed continuous phase of the segment in which the interior diamonds are dispersed, thereby xe2x80x9cresharpeningxe2x80x9d the bit until the entire diamond-impregnated portion of the bit has been consumed. Thus, drill bits with diamond-impregnated segments typically maintain a substantially constant boring rate as long as diamonds remain exposed on such segments.
Conventional impregnated segments typically carry the superabrasive particles in a continuous phase of a hard material, such as tungsten carbide, a tungsten alloy, a metal carbide, a refractory metal alloy, a ceramic, copper, a copper-based alloy, nickel, a nickel-based alloy, cobalt, a cobalt-based alloy, iron, an iron-based alloy, silver, or a silver-based alloy. Such materials are, however, typically relatively brittle and may fracture when subjected to the stresses of drilling. Accordingly, when subjected to the high stresses of drilling, and particularly impact stresses, the continuous phase of such impregnated segments may break, resulting in the premature failure thereof and potentially the premature failure of the bit upon which such segments are carried. Thus, drilling times and costs are increased by premature failure of conventional impregnated segments, as it is necessary to remove the drill string from the bore hole, replace the entire drill bit, and reintroduce the drill string into the bore hole.
U.S. Pat. No. 4,234,048 (the xe2x80x9c""048 patentxe2x80x9d), which issued to David S. Rowley on Nov. 18, 1980, discloses an exemplary drill bit that bears diamond-impregnated segments on the crown thereof. Typically, the impregnated segments of such drill bits are C-shaped or hemispherically shaped, somewhat flat, and arranged somewhat radially around the crown of the drill bit. Each impregnated segment typically extends from the inner cone of the drill bit, over the nose and up the bit face to the gage. The impregnated segments may be attached directly to the drill bit during fabrication or partially disposed within a slot or channel formed into the crown and secured to the drill bit by brazing. When attached to the crown of a drill bit, conventional impregnated segments have a relatively low profile (i.e., shallow recesses between adjacent segments) relative to the bit face and a footprint that covers the majority of the drill bit surface from the nose to the gage. The low profile is typically required due to the relatively brittle materials from which the continuous phases of conventional impregnated segments are formed. Similarly, the generally semicircular shape of conventional impregnated segments and their somewhat radial arrangement around the crown of a bit body are required to prevent the breakage and premature wear of such impregnated segments due to the hard but relatively brittle continuous-phase materials thereof. The large xe2x80x9cfootprintxe2x80x9d of conventional impregnated segment-bearing drill bits is typically necessary to provide a sufficient amount of cutting material on the face of the bit. To some extent, the conventionally required semicircular shape of impregnated segments has also prohibited the use of alternative impregnated segment shapes, drill bit designs, and arrangements of impregnated segments on drill bits, which could otherwise optimize drilling rates and reduce the rate of bit wear and failure.
Because of the low profile or exposure and large surface area footprint of conventional impregnated segments, very little clearance exists between the face of the drill bit and the drilled formation during use of the drill bit upon which such segments are carried. Consequently, the build-up of formation fines, frequently referred to as rock flour, on the impregnated segments may prevent contact of the impregnated segments with the interior surface of the borehole and may reduce the depth of cut of the drill bit.
Moreover, due to the large surface area footprint and the low profile of impregnated segments on conventional drill bits, the hydraulics of such drill bits cannot be fully employed to remove formation fines therefrom or to cool the segments. Therefore, the penetration rate of drilling and the amount of weight on bit that may be employed on the drill bit may both decrease, while the rate of wear will be undesirably high, and failure of the drill bit may occur.
An additional characteristic with conventional impregnated segments having large surface area footprints is that much of the exposed cutting surface of the segments is located a significant lateral distance from the nearest waterway, or area in which drilling-fluid is circulated. Such relatively large lateral distances from the flow of water or drilling fluid thereby impedes the flushing away of cuttings, or fines, from the segment and can aggravate the previously mentioned problems such as the face and crown of the drill bit being built up with sands and fines.
Another problem encountered in the art is that when drilling differing formations or when drilling a formation having soft layers, medium hard layers, and hard layers, it is usually necessary to employ drill bits particularly designed and especially suited for drilling in the layer being encountered in order to ensure steady progress on the well being drilled. Thus, a drilling crew is frequently selecting a drill bit having an appropriate diamond cutter density to balance the rate of penetration (ROP) with wear resistance for extending the useful life of the bit. For example, upon encountering a relatively soft layer, a relatively economical drill bit having a light diamond cutter density particularly suited to drilling soft layers would be used to maximize the rate of bit penetration in the formation. Upon encountering a medium hard layer, a relatively more expensive drill bit having a medium cutter density particularly suited to drilling medium hard layers would be required to maximize the rate of bit penetration in that particular medium hard strata of the formation being drilled. Lastly, upon encountering a hard layer, a yet more expensive drill bit having a high diamond cutter density particularly suited to drilling hard layers would be required to prevent excessive wear of the cutters while allowing a sufficient weight-on-bit that would provide an acceptable ROP through such hard portion of the formation being drilled. Thus, it would be desirable to have a bit that could drill quickly through soft layers and medium layers of a given formation and that could also drill the hard layers of the formation at an acceptable ROP while also providing enhanced wear resistance to extend the useful life of the bit. Such a drill bit would economically benefit the art by decreasing the amount of rig time required to pull a particular drill bit from the well bore being drilled, substitute it with another drill bit more suitable for the particular layer being drilled, and then run the substitute drill bit into the well bore to resume drilling. During the drilling of a well, and depending on the total depth of the well and the number of various hard, medium, and soft layers that a well bore is to pass through until reaching the deepest or most distant zone of interest, several if not many such drill bit substitutions may be required, thereby significantly increasing the overall cost of drilling a well.
U.S. Pat. No. 5,505,272 issued to Ian E. Clark on Apr. 9, 1996, discloses a coring drill bit having cutting inserts made of segments cut from a composite blank wherein a polycrystalline diamond compact (PDC), or, alternatively, polycrystalline cubic boron nitride (PCBN), has been bonded to a tungsten carbide backing. The cut segments are then installed singularly or optionally arranged in clusters of three wherein the PDC or PCBN compact layer of each adjacent segment is differently oriented so as to be exposed to the leading face, the inner gage, or the outer gage, respectively. Additionally, a noncoring drill bit is disclosed wherein inserts protrude slightly from the face of the drill bit and extend from the outer gauge of the face of the bit toward the center of the face and wherein the inner ends of the inserts are at different distances from the central axis of the drill bit.
U.S. Pat. No. 4,128,136 issued to Generoux on Dec. 5, 1978, discloses a diamond coring bit having an annular crown and inner and outer concentric side surfaces. The inner concentric side surface of the crown defines a hollow core in the annular crown of the bit for accommodating a core sample of a subterranean formation. The annular crown is formed from a plurality of radially oriented composite segments impregnated with diamonds radially and circumferentially spaced apart from each other by less abrasive spacer materials.
U.S. Pat. No. 3,106,973 issued to Christensen on Oct. 15, 1963, discloses a drill bit provided with circumferentially and radially spaced apart grooves having cutter blades secured therein. The cutter blades have diamond impregnated sections formed of a matrix of preselected materials.
U.S. Pat. No. 5,147,001 issued to Chow et al. on Sep. 15, 1992, discloses a cutting structure for a drill bit including a substantially planar array of cutting elements arranged in contiguous proximity interrupted by a plurality of discontinuities to minimize and localize residual thermally induced stresses.
Notwithstanding benefits and advantages offered by drill bits including cutting elements incorporating abrasive particles impregnated within matrices of various materials as disclosed in the preceding references, there remains a need within the art for drill bit cutting elements incorporating impregnated segments which will better resist breakage during drilling of very hard and abrasive formations, and which may be optimally designed and arranged upon a drill bit.
There is also a need for cutting elements incorporating impregnated segments which may be strategically arranged on a drill bit to facilitate the use of drill bit hydraulics to remove formation fines from the impregnated surfaces of the drill bit, thereby facilitating the use of alternative and more efficient drill bit designs.
Furthermore, there is a need within the art for a drill bit which can be used to efficiently drill hard, medium, and soft layers of a given formation, or formations, while maximizing the wear resistance of the bit.
A further need within the art is for a drill bit having cutting elements including impregnated segments which can be positioned to have enhanced exposure to waterways or drilling fluid flow paths and channels of the bit to promote better flushing of cutting debris and formation fines away from the area of the segment engaging the formation.
An additional need within the art is for the ability to easily and consistently construct drill bits having cutting elements incorporating impregnated segments therein in preselected patterns and orientations in order to optimize the performance of the drill bit.
Another need within the art is for cutting structure which incorporates segments of abrasive, impregnated, solid matrix material which can readily and consistently be produced in a variety of shapes and nominal thicknesses to best suit a wide variety of drill bits.
The earth-boring drill bits and cutting elements embodying the present invention address the foregoing needs.
The earth-boring drill bits and cutting elements of the present invention are particularly suitable for use with bladed-style drill bits as well as nonbladed drill bits. Preferably, at least one first cutting element segment formed of a continuous-phase solid matrix material impregnated with at least one particulate superabrasive material is juxtapositioned with at least one second cutting element segment formed of a continuous-phase solid matrix material to comprise a laminated cutting element. Preferably, the at least one second segment is essentially devoid of impregnated superabrasive or abrasive particles. Alternatively, the at least one second segment can be impregnated with a preselected, secondary, particulate superabrasive material which results in the at least one second segment being less abrasive and less wear resistant than the at least one first abrasive segment.
Such continuous-phase solid matrices particularly suitable for forming the first and second segments, and not regarded as being superabrasive, include the following: metal carbide, tungsten carbide, tungsten-based alloys, refractory metal alloys, ceramics, copper, copper-based alloys, nickel, nickel-based alloys, cobalt, cobalt-based alloys, iron, iron-based alloys, silver, and silver-based alloys, for example. Such particulate superabrasive materials particularly suitable for impregnation include: natural diamond, synthetic diamond, polycrystalline diamond compact, thermally stable polycrystalline diamond, and cubic boron nitride.
Preferably, the segments have a preselected nominal thickness that can be constant or nonconstant, ranging from a minimum thickness to a maximum thickness. Typically, the nominal thicknesses of the segments are less than approximately 0.5 inches (approximately 12.2 mm) and preferably do not exceed 0.15 inches (3.8 mm). The segments may have a variety of overall configurations including generally rectangular, generally arcuate, generally circular, generally semicircular, and generally serpentine. Furthermore, the segments are arranged in preselected patterns and orientations. Such patterns include at least one first abrasive segment alternating with at least one second, generally superabrasive-free, or lesser abrasive segment. Preferably, the segments are positioned in a preselected pattern extending in a generally radial manner from the longitudinal center of the drill bit toward the gage portion of the bit body or, in the case of being mounted on a blade structure, generally along a selected portion of the blade structure. Furthermore, the individual segments comprising a laminated cutting element can be oriented generally circumferentially, radially, or at an angle with respect to an imaginary reference line to provide a wide variety of cutting elements.
An alternative embodiment of the present invention includes a cutting element adapted for being secured to a blade structure of a bladed-style earth-boring drill bit. The cutting element includes at least one first segment having a preselected overall configuration and a preselected nominal thickness secured to at least one blade structure of a drill bit. For example, a given segment could have a thickness of approximately 0.13 inches (3.3 mm) through one region of the segment and a thickness of approximately 0.5 inches (12.7 mm) through another region of the same segment.
The at least one first segment of the cutting element is comprised of an essentially continuous-phase solid matrix of at least one material impregnated with at least one particulate superabrasive material in at least a portion thereof. Furthermore, the at least one first segment is preferably disposed onto the at least one blade structure in such a manner and orientation to expose at least one lengthwise-extending edge of the at least one first segment to the formation. Additionally, the at least one first segment is located at a preselected distance from, and at a preselected orientation with respect to, an imaginary reference line extending generally along the major axis, or center, of the at least one blade structure. Optionally, the cutting element may be provided with at least one second segment being essentially superabrasive-free and having at least one lengthwise edge exposed and positioned in an end-to-end manner with the at least one first segment. A yet further option includes the at least one second segment being impregnated with a selected particulate superabrasive material which results in the at least one second segment being less abrasive and less abrasion resistant than the at least one first abrasive segment.
Other advantages of the present invention will become apparent to those of ordinary skill in the art through a consideration of the ensuing description, the drawings and the appended claims.